1. Field of the Invention
The present invention relates to a property recovering method for a Ni-base heat resistant alloy whose properties such as strength and ductility have been deteriorated by use at a high temperature.
2. Description of the Related Art
A Ni-base heat resistant alloy which has a .gamma.' intermetallic compound of Ni.sub.3 (Al, Ta, Ti) as a main ingredient and also has a solid solution strengthening function given by precipitation hardening of the second phase and Mo, W, or the like has been used for a high-temperature member such as a moving blade of gas turbine and jet engine. Here, the second phase is a phase containing an intermetallic compound, carbide, and the like. The aforesaid Ni-base heat resistant alloys include a Ni-base heat resistant alloy disclosed in Japanese Patent Provisional Publication No. 6-57359 (No. 57359/1994) (hereinafter referred to as alloy A) and a Ni-base heat resistant alloy commercially available under the tradename Inconel 738 (hereinafter referred to as alloy B). The compositions of these alloys A and B are given in Table 1.
TABLE 1 Chemical composition of material subjected to property recovering treatment in accordance with the present invention (wt %) Element Cr Co Mo W Ta Al Ti C B Alloy A 13.1-15 8.5-10.5 1-3.5 3.5-4.5 3-5.5 3.5-4.5 2.2-3.2 0.06- 0.025 or 0.12 less Alloy B 15.7- 8-9 1.5-2 2.4-2.8 1.5-2 3.2-3.7 3.2-3.7 0.09- 0.007- 16.3 0.13 0.012 Element Zr Mg/Ca Hf Nb Fe Mn Si S Ni Alloy A 0.01- 1-100 1.5 or -- -- -- -- -- Balance 0.05 ppm less Alloy B 0.03- -- -- 0.6-1.1 0.05 or 0.02 or 0.3 or 0.015 or Balance 0.08 less less less less Note) Al + Ti: 6.5-7.2 (Alloy B)
For the Ni-base heat resistant alloy of this type, the second phase (intermetallic compound, carbide, etc.) is coarsened or the diffusion and condensation of impurity elements take place because of heat history due to the long-term use at a high temperature, by which the strength and ductility are decreased. Therefore, the member using such an alloy becomes incapable of being used, and finally must be scrapped because of the formation of cracks. Also, these Ni-base heat resistant alloys are generally very expensive.